The invention relates to a semiconductor device, and more particularly, to a method for forming an isolation structure to uniformly fill trenches of a semiconductor device so as to improve the characteristics of the semiconductor device.
Owing to the development of semiconductor manufacturing technology, very fine patterns can be formed in a semiconductor device using small design rules, and thus the integration level of the semiconductor device can be increased. In manufacturing a semiconductor memory device, such as a direct random access memory (DRAM) having very fine patterns, a device isolation process is important to increase the data retention time of the semiconductor memory device for improving the production yield. Thus, many processes and materials have been studied and developed based on the isolation process to improve the data retention time of a semiconductor device.
Among various isolation processes, a shallow trench isolation (STI) process is widely used since devices can be efficiently isolated using narrow trenches and an isolation layer. In the STI process, trenches are formed in a semiconductor substrate to a predetermined depth through typical exposure and etch processes, and the trenches are filled with an insulation layer. Then, a planarization process is performed on the insulation layer to form an isolation layer in the trenches. To improve gap-fill characteristics for filling trenches, a high density plasma (HDP) oxide layer is used as a gap-fill material or a deposition-etch-deposition (DED) method is used. However, the HDP oxide layer and the DED method are not suitable for filling trenches of a semiconductor device with sub-60 nm technology. In this case, trenches are filled with a flowable insulation layer formed of a compound including a solvent and a solute through a spin on dielectric (SOD) process.
In the SOD process using a flowable insulation layer, a compound including a solvent and a solute is applied to trenches using a coater to form a flowable insulation layer. Next, a curing process is performed to fill the trenches with the flowable insulation layer while densifying the flowable insulation layer. Then, the flowable insulation layer is recessed to a predetermined depth, and a trench isolation layer is formed in the trenches by filling the recessed portions of the flowable insulation layer with a buried insulation layer. However, the SOD process using a flowable insulation layer has many limitations such as the difficulty to uniformly fill the trenches with the trench isolation layer. Therefore, there is a need for an improved method for forming an isolation layer in a semiconductor device to obtain stabile device characteristics.